The present invention relates to aircraft control systems and, in particular, to a flare control system which directs the aircraft onto a specific curvilinear path.
Known landing systems commonly employ a glide slope detector which carries the aircraft to within a certain distance of the landing strip after which a flare coupler is engaged. This flare coupler is commonly controlled by a radar altimeter, a normal accelerometer but no other aircraft sensors. Because of the relatively few controlling parameters, the dispersion of the touchdown point can be relatively large.
Conventional flare couplers attempt to direct an aircraft along an exponential path by keeping the descent rate proportional to altitude. However, these flare couplers do not measure and respond to the longitudinal displacement of the aircraft. As a result, wind gusts and other atmospheric disturbances can deflect the aircraft from the initial exponential path to another one of a family of exponential paths. Therefore, the final touchdown point is uncertain and its scattering will depend upon atmospheric conditions and disturbances.
An important consideration for flare control systems is the effect of noise produced by aircraft sensors controlling the flare maneuver. When only one aircraft sensor is employed to control the flare maneuver, its noise becomes an independent cause of scattering of the touchdown point.
An example of an integrated glide path/flare automatic flight control system is disclosed in U.S. Pat. No. 3,892,373.